1. Field of the Invention
The present invention relates to a backlight unit and a method of manufacturing a polarization film employed in the same. More particularly, the present invention relates to a backlight unit having a polarization film for performing the function of a reflective polarization film and a method of manufacturing the polarization film employed in the same.
2. Description of the Related Art
A Liquid crystal display (hereinafter, referred to as “LCD”) displays an image using change of the transmissivity of liquid crystals in LCD. The LCD is not a self light-emitting device, and so includes a backlight unit (hereinafter, referred to as “BLU”) for providing a light to a panel located over the BLU.
FIG. 1A is a sectional view illustrating the BLU employed in the LCD.
In FIG. 1A, the BLU 100 is driven by edge-light method, and includes a light source unit 110, a light guiding plate 120, a reflector 130, an optical film 140 and a reflective polarization film 148.
The light source unit 110 has at least one cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”) 112 and a light source reflector 114.
The CCFL 112 emits a linear light having a certain wavelength.
A light emitted from the CCFL 112 is reflected by the light source reflector 114 made up of reflective substance and the reflector 130, and then the reflected light is diffused through the whole of the light guiding plate 120 as shown in FIG. 1A.
The optical film 140 includes a diffuser 142, a prism sheet 144 and a protection sheet 146.
The diffuser 142 diffuses or condenses light transmitted from the light guiding plate 120 to maintain constantly the brightness of the BLU 100 and increase the view angle of the LCD.
The prism sheet 144 condenses light transmitted from the diffuser 142 in a direction of the panel so that the brightness of the light transmitted from the BLU 100 to the panel is enhanced.
The protection sheet 146 is located over the prism sheet 144 in order to prevent the prism sheet 144 from dust, etc, and increases the view angle of the LCD narrowed by the prism sheet 144.
Only some of a light provided from the BLU 100 is transmitted through the panel (not shown). For example, P wave of the light provided from the BLU 100 is transmitted through the panel, and S wave of the light is absorbed by the panel. Accordingly, the reflective polarization film 148 is employed in the BLU 100 so as to use the S wave absorbed by the panel.
The reflective polarization film 148 reflects S wave of a light diffused by the protection sheet 146 in the direction of the light guiding plate 120, and provides P wave of the light to the panel.
The S wave reflected by the reflective polarization film 148 is again reflected by the light guiding plate 120 or the reflector 130. As a result, the reflected S wave is changed into light including P wave and S wave.
The changed light is again incident to the reflective polarization film 148 through the diffuser 142, the prism sheet 144 and the protection sheet 146.
The BLU 100 enhances the efficiency of the light by using the above described method.
Hereinafter, the reflective polarization film 148 will be described in detail.
The reflective polarization film 148 included in the BLU 100 employs a thin multi-layered reflective polarization film formed by depositing transparent substances having different refractive index. Here, a representative reflective polarization film 148 is DBEF (dual brightness enhancement film) of 3M Company. However, the thin multi-layered reflective polarization film is not good in the transmission efficiency for a particular wavelength and also is not good in the reflection efficiency for other wavelength. Accordingly, the following reflective polarization film shown in FIG. 1B has been developed so as to enhance the polarization characteristics of the thin multi-layered reflective polarization film.
FIG. 1B is a perspective view illustrating a reflective polarization film employed in the BLU of FIG. 1A.
In FIG. 1B, a reflective polarization film 148 employed in the BLU 100 as a wire grid polarization film is manufactured by forming fine metal patterns 152 on a transparent substrate 150. Here, the metal patterns 152 are formed by forming a metal thin film on the transparent substrate 150, and then irradiating a polarized laser beam on the metal thin film. This is disclosed in Korean application number 2005-40544.
In the above reflective polarization film 148, the interval of the metal patterns 152 should be formed finely so that the reflective polarization film 148 performs desired polarization function. However, it is difficult to form accurately the metal patterns 152 on the transparent substrate 150, and so a process of manufacturing one reflective polarization film 148 has to be long. Accordingly, it is difficult to manufacture in great quantities the reflective polarization film 148.